IrDA is a standard defined by the IrDA consortium. It specifies a way to wirelessly transfer data via infrared radiation. The IrDA specifications include standards for both the physical devices and the protocols they use to communicate with each other. The IrDA standards have arised from the need to connect various mobile devices together as shown by FIG. 1.
IrDA devices communicate using infrared LEDs. The wavelength used is typically 875 nm. IrDA devices conforming to standards IrDA versions 1.0 and 1.1 work over distances up to 1.0 m with a bit error ratio of 10−9 and maximum level of surrounding illumination 10 klux (daylight). Speeds for IrDA version 1.0 range from 2400 to 115200 kbps. IrDA version 1.1 defines speeds 0.576 and 1.152 Mbps, with ¼ mark-to-space ratio. At these speeds, the basic unit (packet) is transmitted synchronously.
A packet consists of two start words followed by target address (IrDA devices are assigned numbers by the means of IrDA protocol, so they are able to unambiguously identify themselves), data, CRC-16 and a stop word. The whole packet (frame) including CRC-16 is generated by IrDA compatible chipset.
For 4 Mbps speed, so-called 4 PPM modulation with ¼ mark-to-space ratio is used. Two bits are encoded in a pulse within one of the four possible positions in time. So, information is carried by the pulse position, instead of pulse existence as in previous modulations. For example, bits “00” would be transmitted as a sequence “1000” (flash-nothing-nothing-nothing), bits “01” would be “0100,” bit “11” would be sent as “0001”.
The main reason for the 4 PPM modulation is the fact, that only half of the LED flashes are needed than in previous modulations; so, data can be transferred two times faster. Also, it is easier for the receiver to maintain the level of surrounding illumination, since a constant number of pulses are received within a given time.
With bit speed of 4 Mbps, the transmitter flashes at 2 MHz rate. However, unlike 0.576 and 1.152 Mbps, 4 Mbps packets use CRC-32 correction code. Most chipsets which can use this modulation can also generate CRC-32 by themselves, and check it when receiving.
An IrDA receiver needs a way to distinguish between the surrounding illumination, noise, and received signal. For this purpose, it is generally useful to use the highest possible output power, since higher power causes a higher current in the receiver which means a better signal-to-noise ratio. However, IR-LEDs cannot transmit at full power continuously over 100% of the time. So, a pulse width of only 3/16 or ¼ (mark-to-space ratio) of the total time for one bit is generally used. Hence, the power can now be up to four or five times the possible maximum power for LEDs shining continuously. Additionally, the transmission path does not carry the dc component, thus it is necessary to use pulse modulation when transmitting.
Several standard protocols used by IrDA devices include IrDA Infrared Link Access Protocol (IrLAP), IrDA Infrared Link Management Protocol (IrLMP); IrDA Transport Protocols (Tiny TP), IrDA Object Exchange Protocol (IrOBEX), Extensions to IrOBEX for Ir Mobile Communications, and IrTran-P (Infrared Transfer Picture) Specification.
Therefore, it is an aspect of the invention to use IrDA technology to wirelessly transmit and receive data to and from a meter, such as a power and/or energy meter for switchboard and billing applications. These meters are generally mounted at a customer location, on an industrial switchboard panel, and on a utility substation. Data is collected from these meters by a meter reader who takes the data off the meter and writes the data on paper. The data is then entered into a billing or energy management software application.
Data can also be read by a serial or Ethernet connection. However, many of the above-mentioned locations do not have this type of capability. Data can also be read by hard-wiring a mobile computing device to the meter. However, this requires the meter reader to physically locate a connection port and connect wires, thereby making the meter reading process time-consuming.